1. Field of the Invention
This invention relates to magnetrons. In particular the invention relates to resonant cavity magnetrons employing a strapped vane anode structure.
2. Description of Related Art
A magnetron of this kind is disclosed in U.S. Pat. No. 4,287,451. This magnetron is shown as having iron or copper strap rings which are used to strap copper vanes. The combinations of materials in the vanes and straps of this specification have been chosen to prevent vane cracking in the event of the expansion of the vanes and strap rings with temperature.
Such magnetrons comprise a cylindrical anode having a plurality of inwardly extending radial vanes which together form multi-resonating cavities. A cathode extends along the axis of the anode forming an interaction space between free edges of the vanes and the cathode. When in use an electric field is generated between the anode and the cathode and a magnetic field along the axis of the andoe. Microwave energy is induced in the cavities between the anode vanes.
The temperature coefficient of frequency of such a magnetron is approximately equal to the temperature coefficient of linear expansion of the anode materials of the magnetron if endspace effects are discounted. This can cause problems whenever magnetrons of this type are to be used in conditions where the ambient temperature can fluctuate. Some reduction in the temperature coefficient of frequency may therefore be achieved by manufacturing the anode from a material having a low coefficient of linear expansion, for example molybdenum. In order to maintain a high figure of merit, Q.sub.o for the magnetron, the microwave conducting surfaces of the anode have to be copper clad, however.